Tunnel valve magnetic tape head for multichannel tape recording

ABSTRACT

An apparatus, according to one embodiment, includes: a plurality of tunnel valve read transducers arranged in an array extending along a read module. Each of the tunnel valve read transducers includes: a sensor structure having a cap layer, a free layer, a tunnel barrier layer, a reference layer and an antiferromagnetic layer, and electrically insulating layers on opposite sides of the sensor structure. Moreover, a height of the free layer measured in a direction perpendicular to a media bearing surface of the read module is less than a width of the free layer measured in a cross-track direction perpendicular to an intended direction of media travel.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to magnetic tape heads havingtunnel valve read transducers with tunnel magnetoresistive (TMR) sensorconfigurations which achieve reduced magnetic noise.

In magnetic storage systems, magnetic transducers read data from andwrite data onto magnetic recording media. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, the drive moves the magnetic tape over thesurface of the tape head at high speed. Usually the tape head isdesigned to minimize the spacing between the head and the tape. Thespacing between the magnetic head and the magnetic tape is crucial andso goals in these systems are to have the recording gaps of thetransducers, which are the source of the magnetic recording flux in nearcontact with the tape to effect writing sharp transitions, and to havethe read elements in near contact with the tape to provide effectivecoupling of the magnetic field from the tape to the read elements.

Minimization of the spacing between the head and the tape, however,induces frequent contact between the tape and the media facing side ofthe head, causing tape operations to be deemed a type of contactrecording. This contact, in view of the high tape speeds and tapeabrasivity, quickly affects the integrity of the materials used to formthe media facing surface of the head, e.g., causing wear thereto,smearing which is known to cause shorts, bending ductility, etc.Furthermore, shorting may occur when an asperity of the tape media dragsany of the conductive metallic films near the sensor across the tunneljunction.

Implementing TMR sensors to read from and/or write to magnetic tape hasalso reduced the shield-to-shield spacing which allows for more detailedreading and/or writing to magnetic tape by allowing the linear densityof transitions on tape to increase. However, this increase has not comewithout drawbacks. For instance, at smaller dimensions, conventionalfree layers have proven to be magnetically unstable, thereby introducingmagnetic switching noise.

SUMMARY

An apparatus, according to one embodiment, includes: a plurality oftunnel valve read transducers arranged in an array extending along aread module. Each of the tunnel valve read transducers includes: asensor structure having a cap layer, a free layer, a tunnel barrierlayer, a reference layer and an antiferromagnetic layer, andelectrically insulating layers on opposite sides of the sensorstructure. Moreover, a height of the free layer measured in a directionperpendicular to a media bearing surface of the read module is less thana width of the free layer measured in a cross-track directionperpendicular to an intended direction of media travel.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2A is a side view of a flat-lapped, bi-directional, two-modulemagnetic tape head according to one embodiment.

FIG. 2B is a tape facing surface view taken from Line 2B of FIG. 2A.

FIG. 2C is a detailed view taken from Circle 2C of FIG. 2B.

FIG. 2D is a detailed view of a partial tape facing surface of a pair ofmodules.

FIG. 3 is a partial tape facing surface view of a magnetic head having awrite-read-write configuration.

FIG. 4 is a partial tape facing surface view of a magnetic head having aread-write-read configuration.

FIG. 5 is a side view of a magnetic tape head with three modulesaccording to one embodiment where the modules all generally lie alongabout parallel planes.

FIG. 6 is a side view of a magnetic tape head with three modules in atangent (angled) configuration.

FIG. 7 is a side view of a magnetic tape head with three modules in anoverwrap configuration.

FIGS. 8A-8C are schematics depicting the principles of tape tenting.

FIG. 9 is a representational diagram of files and indexes stored on amagnetic tape according to one embodiment.

FIG. 10A is a partial tape facing surface view of a magnetic tape headaccording to one embodiment.

FIG. 10B is a partial detailed tape facing surface view of a tunnelvalve read transducer from FIG. 10A.

FIG. 10C is a detailed view of the free layer from FIG. 10B shown alonga plane perpendicular to the plane of deposition of the free layer,according to one embodiment.

FIG. 10D is a detailed view of the sensor structure from FIG. 10B shownalong a plane perpendicular to the plane of deposition of the sensorstructure, according to one embodiment.

FIG. 10E is a partial detailed tape facing surface view of a tunnelvalve read transducer according to one embodiment.

FIG. 10F is a detailed view of the free layer and hard bias magnets fromFIG. 10E shown along a plane perpendicular to the plane of deposition ofthe free layer and the hard bias magnets, according to one embodiment.

FIG. 10G is a partial detailed tape facing surface view of a tunnelvalve read transducer according to one embodiment.

FIG. 11A is a partial detailed view of a hard bias structure and a freelayer according to the prior art.

FIG. 11B is a partial detailed view of a hard bias magnet and a freelayer according to one embodiment.

FIG. 11C is a partial detailed view of a hard bias magnet and a freelayer according to one embodiment.

FIG. 12 is a graph plotting the calculated magnetization of the freelayer for each of the structures in FIGS. 11A-11C vs. the distance fromthe sensor edge.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof, which include improved free layer performance. Shape anisotropyresulting from free layer dimensions and/or the introduction of hardbias magnets as described herein may be able to provide a desirablelevel of stabilization to the free layer, and thereby achieve unexpectedimprovements over conventional implementations, e.g., as will bedescribed in further detail below.

In one general embodiment, an apparatus includes: a tape head having: awrite module, a read module, and a plurality of tunnel valve readtransducers arranged in an array extending along the read module. Eachof the tunnel valve read transducers includes: a sensor structure, anupper magnetic shield, a lower magnetic shield, an upper conductingspacer layer between the sensor structure and the upper magnetic shield,a lower conducting spacer layer between the sensor structure and thelower magnetic shield, and electrically insulating layers on oppositesides of the sensor structure. The sensor structure includes a caplayer, a free layer, a tunnel barrier layer, a reference layer and anantiferromagnetic layer. Moreover, a height of the free layer measuredin a direction perpendicular to a media bearing surface of the readmodule is less than a width of the free layer measured in a cross-trackdirection perpendicular to an intended direction of media travel.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the drive 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may include at least oneservo channel and at least one data channel, each of which include dataflow processing logic configured to process and/or store information tobe written to and/or read from the tape 122. The controller 128 mayoperate under logic known in the art, as well as any logic disclosedherein, and thus may be considered as a processor for any of thedescriptions of tape drives included herein, in various embodiments. Thecontroller 128 may be coupled to a memory 136 of any known type, whichmay store instructions executable by the controller 128. Moreover, thecontroller 128 may be configured and/or programmable to perform orcontrol some or all of the methodology presented herein. Thus, thecontroller 128 may be considered to be configured to perform variousoperations by way of logic programmed into one or more chips, modules,and/or blocks; software, firmware, and/or other instructions beingavailable to one or more processors; etc., and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (internal or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, read-only memory (ROM) device, etc., embedded intoor coupled to the inside or outside of the tape cartridge 150. Thenonvolatile memory is accessible by the tape drive and the tapeoperating software (the driver software), and/or another device.

By way of example, FIG. 2A illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 3 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B may be made of the sameor similar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration includes a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationincludes one reader shield in the same physical layer as one writer pole(hence, “merged”). The readers and writers may also be arranged in aninterleaved configuration. Alternatively, each array of channels may bereaders or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2B illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2B of FIG. 2A. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 32 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2B on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2C depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2C of FIG. 2B. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2C, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2A and 2B-2C together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2D shows a partial tape bearing surface view of complementarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write transducer 214 and the readers, exemplified by the readtransducer 216, are aligned parallel to an intended direction of travelof a tape medium thereacross to form an R/W pair, exemplified by the R/Wpair 222. Note that the intended direction of tape travel is sometimesreferred to herein as the direction of tape travel, and such terms maybe used interchangeably. Such direction of tape travel may be inferredfrom the design of the system, e.g., by examining the guides; observingthe actual direction of tape travel relative to the reference point;etc. Moreover, in a system operable for bi-direction reading and/orwriting, the direction of tape travel in both directions is typicallyparallel and thus both directions may be considered equivalent to eachother.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked magnetoresistive (MR) headassembly 200 includes two thin-film modules 224 and 226 of generallyidentical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (−),cobalt zirconium tantalum (CZT) or Al—Fe—Si (Sendust), a sensor 234 forsensing a data track on a magnetic medium, a second shield 238 typicallyof a nickel-iron alloy (e.g., ˜80/20 at % NiFe, also known aspermalloy), first and second writer pole tips 228, 230, and a coil (notshown). The sensor may be of any known type, including those based onMR, GMR, AMR, TMR, etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 252, 256 each include one or morearrays of writers 260. The inner module 254 of FIG. 3 includes one ormore arrays of readers 258 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

FIG. 5 illustrates a magnetic head 126 according to one embodiment ofthe present invention that includes first, second and third modules 302,304, 306 each having a tape bearing surface 308, 310, 312 respectively,which may be flat, contoured, etc. Note that while the term “tapebearing surface” appears to imply that the surface facing the tape 315is in physical contact with the tape bearing surface, this is notnecessarily the case. Rather, only a portion of the tape may be incontact with the tape bearing surface, constantly or intermittently,with other portions of the tape riding (or “flying”) above the tapebearing surface on a layer of air, sometimes referred to as an “airbearing”. The first module 302 will be referred to as the “leading”module as it is the first module encountered by the tape in a threemodule design for tape moving in the indicated direction. The thirdmodule 306 will be referred to as the “trailing” module. The trailingmodule follows the middle module and is the last module seen by the tapein a three module design. The leading and trailing modules 302, 306 arereferred to collectively as outer modules. Also note that the outermodules 302, 306 will alternate as leading modules, depending on thedirection of travel of the tape 315.

In one embodiment, the tape bearing surfaces 308, 310, 312 of the first,second and third modules 302, 304, 306 lie on about parallel planes(which is meant to include parallel and nearly parallel planes, e.g.,between parallel and tangential as in FIG. 6), and the tape bearingsurface 310 of the second module 304 is above the tape bearing surfaces308, 312 of the first and third modules 302, 306. As described below,this has the effect of creating the desired wrap angle α₂ of the taperelative to the tape bearing surface 310 of the second module 304.

Where the tape bearing surfaces 308, 310, 312 lie along parallel ornearly parallel yet offset planes, intuitively, the tape should peel offof the tape bearing surface 308 of the leading module 302. However, thevacuum created by the skiving edge 318 of the leading module 302 hasbeen found by experimentation to be sufficient to keep the tape adheredto the tape bearing surface 308 of the leading module 302. The trailingedge 320 of the leading module 302 (the end from which the tape leavesthe leading module 302) is the approximate reference point which definesthe wrap angle α₂ over the tape bearing surface 310 of the second module304. The tape stays in close proximity to the tape bearing surface untilclose to the trailing edge 320 of the leading module 302. Accordingly,read and/or write elements 322 may be located near the trailing edges ofthe outer modules 302, 306. These embodiments are particularly adaptedfor write-read-write applications.

A benefit of this and other embodiments described herein is that,because the outer modules 302, 306 are fixed at a determined offset fromthe second module 304, the inner wrap angle α₂ is fixed when the modules302, 304, 306 are coupled together or are otherwise fixed into a head.The inner wrap angle α₂ is approximately tan⁻¹(δ/W) where δ is theheight difference between the planes of the tape bearing surfaces 308,310 and W is the width between the opposing ends of the tape bearingsurfaces 308, 310. An illustrative inner wrap angle α₂ is in a range ofabout 0.3° to about 1.1°, though can be any angle required by thedesign.

Beneficially, the inner wrap angle α₂ on the side of the module 304receiving the tape (leading edge) will be larger than the inner wrapangle α₃ on the trailing edge, as the tape 315 rides above the trailingmodule 306. This difference is generally beneficial as a smaller α₃tends to oppose what has heretofore been a steeper exiting effectivewrap angle.

Note that the tape bearing surfaces 308, 312 of the outer modules 302,306 are positioned to achieve a negative wrap angle at the trailing edge320 of the leading module 302. This is generally beneficial in helpingto reduce friction due to contact with the trailing edge 320, providedthat proper consideration is given to the location of the crowbar regionthat forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements on theleading module 302. Further, at the trailing module 306, the tape 315flies over the tape bearing surface 312 so there is virtually no wear onthe elements when tape is moving in this direction. Particularly, thetape 315 entrains air and so will not significantly ride on the tapebearing surface 312 of the third module 306 (some contact may occur).This is permissible, because the leading module 302 is writing while thetrailing module 306 is idle.

Writing and reading functions are performed by different modules at anygiven time. In one embodiment, the second module 304 includes aplurality of data and optional servo readers 331 and no writers. Thefirst and third modules 302, 306 include a plurality of writers 322 andno data readers, with the exception that the outer modules 302, 306 mayinclude optional servo readers. The servo readers may be used toposition the head during reading and/or writing operations. The servoreader(s) on each module are typically located toward the end of thearray of readers or writers.

By having only readers or side by side writers and servo readers in thegap between the substrate and closure, the gap length can besubstantially reduced. Typical heads have piggybacked readers andwriters, where the writer is formed above each reader. A typical gap is20-35 microns. However, irregularities on the tape may tend to droopinto the gap and create gap erosion. Thus, the smaller the gap is thebetter. The smaller gap enabled herein exhibits fewer wear relatedproblems.

In some embodiments, the second module 304 has a closure, while thefirst and third modules 302, 306 do not have a closure. Where there isno closure, preferably a hard coating is added to the module. Onepreferred coating is diamond-like carbon (DLC).

In the embodiment shown in FIG. 5, the first, second, and third modules302, 304, 306 each have a closure 332, 334, 336, which extends the tapebearing surface of the associated module, thereby effectivelypositioning the read/write elements away from the edge of the tapebearing surface. The closure 332 on the second module 304 can be aceramic closure of a type typically found on tape heads. The closures334, 336 of the first and third modules 302, 306, however, may beshorter than the closure 332 of the second module 304 as measuredparallel to a direction of tape travel over the respective module. Thisenables positioning the modules closer together. One way to produceshorter closures 334, 336 is to lap the standard ceramic closures of thesecond module 304 an additional amount. Another way is to plate ordeposit thin film closures above the elements during thin filmprocessing. For example, a thin film closure of a hard material such asSendust or nickel-iron alloy (e.g., 45/55) can be formed on the module.

With reduced-thickness ceramic or thin film closures 334, 336 or noclosures on the outer modules 302, 306, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan commonly-used linear tape open (LTO) tape head spacing. The openspace between the modules 302, 304, 306 can still be set toapproximately 0.5 to 0.6 mm, which in some embodiments is ideal forstabilizing tape motion over the second module 304.

Depending on tape tension and stiffness, it may be desirable to anglethe tape bearing surfaces of the outer modules relative to the tapebearing surface of the second module. FIG. 6 illustrates an embodimentwhere the modules 302, 304, 306 are in a tangent or nearly tangent(angled) configuration. Particularly, the tape bearing surfaces of theouter modules 302, 306 are about parallel to the tape at the desiredwrap angle α₂ of the second module 304. In other words, the planes ofthe tape bearing surfaces 308, 312 of the outer modules 302, 306 areoriented at about the desired wrap angle α₂ of the tape 315 relative tothe second module 304. The tape will also pop off of the trailing module306 in this embodiment, thereby reducing wear on the elements in thetrailing module 306. These embodiments are particularly useful forwrite-read-write applications. Additional aspects of these embodimentsare similar to those given above.

Typically, the tape wrap angles may be set about midway between theembodiments shown in FIGS. 5 and 6.

FIG. 7 illustrates an embodiment where the modules 302, 304, 306 are inan overwrap configuration. Particularly, the tape bearing surfaces 308,312 of the outer modules 302, 306 are angled slightly more than the tape315 when set at the desired wrap angle α₂ relative to the second module304. In this embodiment, the tape does not pop off of the trailingmodule, allowing it to be used for writing or reading. Accordingly, theleading and middle modules can both perform reading and/or writingfunctions while the trailing module can read any just-written data.Thus, these embodiments are preferred for write-read-write,read-write-read, and write-write-read applications. In the latterembodiments, closures should be wider than the tape canopies forensuring read capability. The wider closures may require a widergap-to-gap separation. Therefore, a preferred embodiment has awrite-read-write configuration, which may use shortened closures thatthus allow closer gap-to-gap separation.

Additional aspects of the embodiments shown in FIGS. 6 and 7 are similarto those given above.

A 32 channel version of a multi-module head 126 may use cables 350having leads on the same or smaller pitch as current 16 channelpiggyback LTO modules, or alternatively the connections on the modulemay be organ-keyboarded for a 50% reduction in cable span. Over-under,writing pair unshielded cables may be used for the writers, which mayhave integrated servo readers.

The outer wrap angles α₁ may be set in the drive, such as by guides ofany type known in the art, such as adjustable rollers, slides, etc. oralternatively by outriggers, which are integral to the head. Forexample, rollers having an offset axis may be used to set the wrapangles. The offset axis creates an orbital arc of rotation, allowingprecise alignment of the wrap angle α₁.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head may bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads. Moreover, unless otherwisespecified, processes and materials of types known in the art may beadapted for use in various embodiments in conformance with the teachingsherein, as would become apparent to one skilled in the art upon readingthe present disclosure.

As a tape is run over a module, it is preferred that the tape passessufficiently close to magnetic transducers on the module such thatreading and/or writing is efficiently performed, e.g., with a low errorrate. According to some approaches, tape tenting may be used to ensurethe tape passes sufficiently close to the portion of the module havingthe magnetic transducers. To better understand this process, FIGS. 8A-8Cillustrate the principles of tape tenting. FIG. 8A shows a module 800having an upper tape bearing surface 802 extending between oppositeedges 804, 806. A stationary tape 808 is shown wrapping around the edges804, 806. As shown, the bending stiffness of the tape 808 lifts the tapeoff of the tape bearing surface 802. Tape tension tends to flatten thetape profile, as shown in FIG. 8A. Where tape tension is minimal, thecurvature of the tape is more parabolic than shown.

FIG. 8B depicts the tape 808 in motion. The leading edge, i.e., thefirst edge the tape encounters when moving, may serve to skive air fromthe tape, thereby creating a subambient air pressure between the tape808 and the tape bearing surface 802. In FIG. 8B, the leading edge isthe left edge and the right edge is the trailing edge when the tape ismoving left to right. As a result, atmospheric pressure above the tapeurges the tape toward the tape bearing surface 802, thereby creatingtape tenting proximate each of the edges. The tape bending stiffnessresists the effect of the atmospheric pressure, thereby causing the tapetenting proximate both the leading and trailing edges. Modeling predictsthat the two tents are very similar in shape.

FIG. 8C depicts how the subambient pressure urges the tape 808 towardthe tape bearing surface 802 even when a trailing guide 810 ispositioned above the plane of the tape bearing surface.

It follows that tape tenting may be used to direct the path of a tape asit passes over a module. As previously mentioned, tape tenting may beused to ensure the tape passes sufficiently close to the portion of themodule having the magnetic transducers, preferably such that readingand/or writing is efficiently performed, e.g., with a low error rate.

Magnetic tapes may be stored in tape cartridges that are, in turn,stored at storage slots or the like inside a data storage library. Thetape cartridges may be stored in the library such that they areaccessible for physical retrieval. In addition to magnetic tapes andtape cartridges, data storage libraries may include data storage drivesthat store data to, and/or retrieve data from, the magnetic tapes.Moreover, tape libraries and the components included therein mayimplement a file system which enables access to tape and data stored onthe tape.

File systems may be used to control how data is stored in, and retrievedfrom, memory. Thus, a file system may include the processes and datastructures that an operating system uses to keep track of files inmemory, e.g., the way the files are organized in memory. Linear TapeFile System (LTFS) is an exemplary format of a file system that may beimplemented in a given library in order to enables access to complianttapes. It should be appreciated that various embodiments herein can beimplemented with a wide range of file system formats, including forexample IBM Spectrum Archive Library Edition (LTFS LE). However, toprovide a context, and solely to assist the reader, some of theembodiments below may be described with reference to LTFS which is atype of file system format. This has been done by way of example only,and should not be deemed limiting on the invention defined in theclaims.

A tape cartridge may be “loaded” by inserting the cartridge into thetape drive, and the tape cartridge may be “unloaded” by removing thetape cartridge from the tape drive. Once loaded in a tape drive, thetape in the cartridge may be “threaded” through the drive by physicallypulling the tape (the magnetic recording portion) from the tapecartridge, and passing it above a magnetic head of a tape drive.Furthermore, the tape may be attached on a take-up reel (e.g., see 121of FIG. 1A above) to move the tape over the magnetic head.

Once threaded in the tape drive, the tape in the cartridge may be“mounted” by reading metadata on a tape and bringing the tape into astate where the LTFS is able to use the tape as a constituent componentof a file system. Moreover, in order to “unmount” a tape, metadata ispreferably first written on the tape (e.g., as an index), after whichthe tape may be removed from the state where the LTFS is allowed to usethe tape as a constituent component of a file system. Finally, to“unthread” the tape, the tape is unattached from the take-up reel and isphysically placed back into the inside of a tape cartridge again. Thecartridge may remain loaded in the tape drive even after the tape hasbeen unthreaded, e.g., waiting for another read and/or write request.However, in other instances, the tape cartridge may be unloaded from thetape drive upon the tape being unthreaded, e.g., as described above.

Magnetic tape is a sequential access medium. Thus, new data is writtento the tape by appending the data at the end of previously written data.It follows that when data is recorded in a tape having only onepartition, metadata (e.g., allocation information) is continuouslyappended to an end of the previously written data as it frequentlyupdates and is accordingly rewritten to tape. As a result, the rearmostinformation is read when a tape is first mounted in order to access themost recent copy of the metadata corresponding to the tape. However,this introduces a considerable amount of delay in the process ofmounting a given tape.

To overcome this delay caused by single partition tape mediums, the LTFSformat includes a tape that is divided into two partitions, whichinclude an index partition and a data partition. The index partition maybe configured to record metadata (meta information), e.g., such as fileallocation information (Index), while the data partition may beconfigured to record the body of the data, e.g., the data itself.

Looking to FIG. 9, a magnetic tape 900 having an index partition 902 anda data partition 904 is illustrated according to one embodiment. Asshown, data files and indexes are stored on the tape. The LTFS formatallows for index information to be recorded in the index partition 902at the beginning of tape 906, as would be appreciated by one skilled inthe art upon reading the present description.

As index information is updated, it preferably overwrites the previousversion of the index information, thereby allowing the currently updatedindex information to be accessible at the beginning of tape in the indexpartition. According to the specific example illustrated in FIG. 9, amost recent version of metadata Index 3 is recorded in the indexpartition 902 at the beginning of the tape 906. Conversely, all threeversion of metadata Index 1, Index 2, Index 3 as well as data File A,File B, File C, File D are recorded in the data partition 904 of thetape. Although Index 1 and Index 2 are old (e.g., outdated) indexes,because information is written to tape by appending it to the end of thepreviously written data as described above, these old indexes Index 1,Index 2 remain stored on the tape 900 in the data partition 904 withoutbeing overwritten.

The metadata may be updated in the index partition 902 and/or the datapartition 904 differently depending on the desired embodiment. Accordingto some embodiments, the metadata of the index partition 902 may beupdated in response to the tape being unmounted, e.g., such that theindex may be read from the index partition when that tape is mountedagain. The metadata may also be written in the data partition 902 so thetape may be mounted using the metadata recorded in the data partition902, e.g., as a backup option.

According to one example, which is no way intended to limit theinvention, LTFS LE may be used to provide the functionality of writingan index in the data partition when a user explicitly instructs thesystem to do so, or at a time designated by a predetermined period whichmay be set by the user, e.g., such that data loss in the event of suddenpower stoppage can be mitigated.

As alluded to above, there is a need to address the issue of magneticnoise as experienced in conventional magnetic tape heads due tothermally and/or magnetically induced switching of unstable domains infree layers thereof. To overcome such issues, some of the embodimentsincluded herein provide magnetic tape heads which include modules havingtunnel valve transducers with free layers having favorable dimensions inorder to achieve shape anisotropy. Moreover, other embodiments includedherein provide magnetic tape heads which include modules having tunnelvalve transducers with hard bias magnets. It follows that variousembodiments included herein achieve a resulting structure which is bothstructurally and functionally different than those seen in conventionaltape and/or hard disk drive (HDD) heads.

Efficient operation (e.g., without exhibiting noise caused by magneticinstability) of the multiple transducers included on a given magnetictape module is greatly desired in order to maintain functionality of theoverall magnetic tape head. However, this constraint is not realized byHDD heads. While the multiple magnetic tape transducers on a givenmagnetic tape module are included on a single die, HDD heads implementsingle channel dies. Therefore, HDD sensors may individually be rejected(yielded out) in response to magnetic instability disrupting readbacksignal quality, while magnetic tape sensors may not. For example, a 1%HDD sensor reject rate (perhaps typical for modern TMR HDD heads) due tonoisy sensors may be an acceptable production loss for HDD heads.However, the same 1% sensor rejection rate would statistically translateto a 28% magnetic tape module reject rate for modules containing 33 datareader sensors. In response, an acceptable magnetic tape sensor rejectrate may be limited to less than 0.03%, thereby resulting in a less than1% magnetic tape module rejection rate. Therefore, it is greatly desiredthat each of the plurality of transducers included on a given module(e.g., on a single die) operate efficiently in order to maintainfunctionality of the overall magnetic tape head. However, a magnetictape sensor reject rate of less than 0.03% was previously thought to noteven be possible for TMR sensors, due, in part, to magnetic instabilityof the free layers thereof.

As described herein, free layer slab dimensions may be able to cause thefree layer to form a largely homogeneous single magnetic domain alignedalong the cross-track direction as a result of shape anisotropy. Thismay directly result in improved sensor performance and overall increasedefficiency of a magnetic head, thereby achieving a significantimprovement compared to conventional implementations.

However, in some instances, such as sensors having non-ideal shapeanisotropy may also give rise to distortions of the magnetic alignmentnear the lateral edges of the domain. In these edge regions, the freelayer magnetization may be locally torqued by demagnetizations fieldstowards a direction perpendicular to the air-bearing surface.Energetically, this causes bifurcation in the magnetic state at thelateral edges, and switching between these states may occur under theimpulse of an external field transient (e.g. fringing fields fromwritten tape traveling thereover) and/or thermal agitation. Suchswitching events undesirably translate into noise in the readbacksignal.

Biasing the entire free layer to this state of alignment may serve as afirst purpose for using hard bias magnets in such instances,particularly as free layer slab dimensions typical for sensors in HDDsmay not able to form a magnetization which is sufficiently homogeneous,and with a singly-aligned domain absent the implementation of hard biasmagnets.

A further purpose of implementing hard bias magnets is to subject thesedistorted edge regions of the free layer to a magnetic field whichfavors torqueing their magnetic orientation back to being about parallelto the cross-track direction. The magnetic field from the hard biasmagnets is preferably strong enough to dominate over the localdemagnetization fields. The resulting magnetization of the free layermay thereby be influenced such that it constitutes a more homogeneoussingle domain. The edge regions may also be stabilized in the sense thatthey are held to this orientation and bifurcated-energy states aresuppressed.

Applying a relatively weak magnetic bias to the edge regions of a freelayer may create more split states resulting in an upshift of thespectral response of noise in the sensor, especially absent desirableshape anisotropy. However, increasing magnetic hard bias strength toovercome this may attenuate signal sensitivity. Thus, choosing thestrength of the hard bias magnets involves a compromise between noiseand signal strength. For instance, implementing relatively stronger hardbias magnets may decrease the sensitivity of the free layer particularlyin the edge regions (which are a significant source of noise), but mayalso shift the spectral characteristics of the noise processes such thatsystem signal to noise ratio (SNR) is less affected. Conversely, whilerelatively weaker hard bias magnets allow for retaining better overallsignal sensitivity, it comes at a cost in noise performance due to aless homogeneous free layer domain which may include states betweenwhich switching can occur.

For reference, sensors implemented in HDDs have small width dimensions(about 50 nm) compared to the length scale of flux leakage toward theshields, resulting in little variation of the field strength from thehard bias across the width of the HDD sensor. There is therefore littlelatitude to engineer a high-susceptibility sensing region at the centerof the free layer separate from low-susceptibility regions at the edges.Overall sensitivity being at a premium for HDDs, the compromise maygenerally gravitate towards implementing a moderate-to-small strengthhard bias.

On the contrary, magnetic sensors for magnetic tape typically havewidths that are much larger than the length scale of flux leakage towardthe shields. According to an example, the width of a magnetic tapesensor may be about 1.5 μm, while the length scale of flux leakagetoward the shields may be about 200 nm for a shield to shield spacing ofabout 100 nm. As a result, the outer edge regions of a free layer in thesensor stack may be strongly anchored in order to reduce noise.Moreover, this may be achieved while also exploiting the relativelysteep decay of the hard bias field strength over distance from the freelayer edges, thereby leaving the susceptibility largely unmodified nearthe central region of the free layer along its longitudinal axis. As aresult, the effective magnetic width and the signal output of the sensormay be decreased moderately, e.g., by an amount in proportion with thewidth of the edge regions, whereas its noise performance may besignificantly improved.

It follows that hard bias magnets may be used to stabilize a free layerand reduce magnetic switching noise in some of the embodiments describedherein. However, due to the reduced field overlap between hard biasmagnet pairs, and given that the peak bias strength corresponding toachieving optimal biasing conditions for a tape sensor is likely largerthan that for an HDD, desirable biasing strengths are not achievable fortape simply by performing incremental changes to conventional HDD hardbias geometry. In sharp contrast to traditional structures andconventional wisdom, various embodiments described herein include newgeometric characteristics for free layers and hard bias layers, each ofwhich are able to achieve substantial improvements over conventionalimplementations. Moreover, these substantial improvements may be evenfurther expounded upon by implementing desirable characteristics of thelayers in the sensor stack as well, e.g., as will be described infurther detail below.

FIGS. 10A-10B depict an apparatus 1000 in accordance with oneembodiment. As an option, the present apparatus 1000 may be implementedin conjunction with features from any other embodiment listed herein,such as those described with reference to the other FIGS. However, suchapparatus 1000 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, theapparatus 1000 presented herein may be used in any desired environment.Thus FIGS. 10A-10B (and the other FIGS.) may be deemed to include anypossible permutation.

It should also be noted that additional layers may be present, andunless otherwise specified, the various layers in this and otherembodiments may be formed using conventional processes. Additionally,the different figures are not drawn to scale, but rather features mayhave been exaggerated to help exemplify the descriptions herein.

As shown in FIG. 10A, apparatus 1000 includes a magnetic tape head 1002.It follows that magnetic tape head 1002 may be able to read and/or writedata to a magnetic tape being passed thereover (e.g., see tape head 126of FIG. 1A). Thus, the magnetic tape head 1002 may include a surfacewhich magnetic tapes come into contact with and are run across or over(e.g., see FIGS. 8A-8C) while reading from and/or writing to themagnetic tape. This surface may also be referred to as a tape bearingsurface of the magnetic tape head 1002.

With continued reference to FIG. 10A, the magnetic tape head 1002includes a read module 1004, which is preferably able to at least readdata from a magnetic tape. In other words, read module 1004 ispreferably a reading module. Accordingly, the read module 1004 (e.g., adie) includes a plurality of concurrent tunnel valve read transducers1006 for reading data from data tracks on a magnetic tape. As shown, theplurality of tunnel valve read transducers 1006 are arranged in an arraywhich extends along a longitudinal axis 1008 of the read module 1004.Furthermore, in some approaches the read module 1004 may further includetunnel valve transducers which are positioned and configured to readdata written to servo patterns (e.g., see servo readers 212 of FIG.2B-2C). In some approaches the magnetic tape head 1002 may also includea write module (not show) capable of writing data to a magnetic tape,e.g., see FIGS. 2A-7.

The plurality of tunnel valve read transducers 1006 also share a commonmedia facing surface 1005 of the read module 1004. In some approaches,the media facing surface 1005 of the read module 1004 may form at leasta portion of the tape bearing surface of the magnetic tape head 1002.Only a partial view of the media facing surface 1005 of the read module1004 is illustrated in FIG. 10A, and therefore not all of the pluralityof tunnel valve read transducers 1006 are shown. In some approaches, theplurality of tunnel valve read transducers 1006 may include 35 tunnelvalve read transducers 1006, each of which is preferably configured toread a respective data or servo track concurrently. For example, 33 ofthe tunnel valve read transducers 1006 may be configured to read arespective data track, while 2 of the tunnel valve read transducers 1006may be configured to read a respective servo track. In other approaches,the plurality of tunnel valve read transducers 1006 may include 65tunnel valve read transducers 1006, each of which is again preferablyconfigured to read a respective data or servo track concurrently. Itfollows that the number of the plurality of tunnel valve readtransducers 1006 included in a magnetic tape head 1002 may depend on thedesired embodiment. Moreover, the plurality of tunnel valve readtransducers 1006 may be positioned and/or configured according to any ofthe approaches described herein.

According to the present embodiment, no write transducers are present onthe common media facing surface 1005, or even the read module 1004itself. However, it should be noted that in other embodiments, an arrayof write transducers may also be included on read module 1004, on anadjacent module, etc., e.g., as shown in any one or more of FIGS. 2A-7.Thus, according to an illustrative approach, a plurality of writetransducers may be arranged in a second array along the module, thesecond array being substantially parallel with the array of tunnel valveread transducers 1006 along the longitudinal axis 1008 of the readmodule 1004. Moreover, in a further approach, the plurality of tunnelvalve read transducers 1006 and the plurality of write transducers mayhave a piggyback configuration (e.g., as seen in FIG. 2C). Furthermore,in some embodiments, the apparatus 1000 may include a drive mechanismfor passing a magnetic medium over the magnetic tape head, e.g., see 100of FIG. 1A, and a controller electrically coupled to the sensor, e.g.,see 128 of FIG. 1A.

Looking now to FIG. 10B, a partial detailed view of the tape facingsurface of one of the tunnel valve read transducers 1006 in FIG. 10A isshown according to one embodiment. It should be noted that although apartial detailed view of only one of the tunnel valve read transducers1006 is shown, any one or more of the tunnel valve read transducers 1006included on read module 1004 of FIG. 10A may have the same or a similarconstruction.

As shown, the tunnel valve read transducer 1006 includes a sensorstructure 1012 as well as upper and lower magnetic shields 1014, 1016respectively, which flank (sandwich) the sensor structure 1012. Theseparation between the upper and lower magnetic shields 1014, 1016proximate to the sensor and measured along the intended direction oftape (e.g., media) travel 1050 is preferably less than about 120 nm, butcould be lower or higher depending on the embodiment. Moreover, upperand lower electrically conductive, non-magnetic spacer layers 1018, 1020are positioned between the sensor structure 1012 and the magneticshields 1014, 1016, respectively.

Between the non-magnetic conductive spacer layers 1018, 1020, the sensorstructure 1012 includes an antiferromagnetic layer 1022 and has a sensorcap layer 1024. The sensor structure 1012 also preferably has an activeTMR region. Thus, the sensor structure 1012 is shown as also including afree layer 1026, a tunnel barrier layer 1028 and a reference layer 1030.According to various embodiments, the free layer 1026, the tunnelbarrier layer 1028 and/or the reference layer 1030 may includeconstruction parameters, e.g., materials, dimensions, properties, etc.,according to any of the embodiments described herein, and/orconventional construction parameters, depending on the desiredembodiment. Illustrative materials for the tunnel barrier layer 1028include amorphous and/or crystalline forms of, but are not limited to,TiOx, MgO and Al₂O₃.

It should be noted that magnetic tape heads are unique in that magnetictape sensor widths may be about 30 to about 50 times greater thantransducer widths for HDD heads. Accordingly, the width of layersincluded in each magnetic tape sensor may be about 30 to about 50 timesgreater than transducer layer widths for HDD heads. For example,magnetic tape sensors corresponding to products having a tape cartridgecapacity in the range of 15 TB are approximately 1 μm wide. However,modern HDD sensors are only approximately 30 nm wide, and are thus aremore than 30 times narrower than some magnetic tape sensors.

Looking to the present embodiment in FIG. 10B, a width of any of thelayers in the sensor structure 1012 may be between about 0.3 μm andabout 1.5 μm. Thus, a width W_(FL) of the free layer of each of thetunnel valve read transducers 1006 may be between about 0.3 μm and about1.5 μm, but could be wider or narrower depending on the desiredembodiment. Magnetic tape head sensors having free layer widths in thisrange may benefit from increased hard bias fields, which is in sharpcontrast to the adverse effects realized by narrower HDD sensors inresponse to increased hard bias fields, e.g., due to the differentmagnetic characteristics along the width of the free layer. Moreover,implementing free layers 1026 in each of the tunnel valve readtransducers 1006 having widths in the above mentioned range may alsoovercome manufacturing challenges limiting the ability to maintain adesirably high sensor width-to-height aspect ratio (e.g. greater thanabout 3), which may have an association with magnetic instability, asrecently discovered by one of the inventors.

The tunnel valve read transducer 1006 illustrated in FIG. 10B furtherincludes electrically insulating layers 1034 on opposite sides of thesensor structure 1012. The electrically insulating layers 1034 separatethe upper conducting spacer layer 1018 from the lower conducting spacerlayer 1020 and the sensor structure 1012 to avoid electrical shortingtherebetween. According to some approaches, the thickness t₁ of theelectrically insulating layers 1034 may be less than about 8 nm, but maybe higher or lower depending on the desired embodiment. Moreover, it ispreferred that the electrically insulating layers 1034 include adielectric material.

Looking to FIG. 10C, a view of the free layer 1026 of FIG. 10B is shownalong a plane perpendicular to the plane of deposition of the free layer1026. Arrows indicating the cross-track direction 1052 and the intendeddirection of tape travel 1050 have been added for reference. As shown,the height H_(FL) of the free layer 1026 is less than the width W_(FL)of the free layer 1026. As shown, the height H_(FL) of the free layer1026 is measured in a direction perpendicular to a media bearing surfaceof the module shown in FIGS. 10A-10B. As mentioned above, the widthW_(FL) of the free layer 1026 may be between about 0.3 μm and about 1.5μm According to an illustrative approach, which is in no way intended tolimit the invention, the width W_(FL) of the free layer 1026 may be lessthan about 2 μm, but could be higher or lower depending on the desiredapproach. As mentioned above, free layer slab dimensions may be able tocause the free layer to form a largely homogeneous single magneticdomain aligned along the cross-track direction as a result of shapeanisotropy alone. This may directly result in improved sensorperformance and overall increased efficiency of a magnetic head. This isa significant improvement compared to conventional implementations whichare unable to implement free layers having a width and height as shownin FIG. 10C.

The general shape of the free layer shown in FIG. 10C may also translateto the height and width of the overall sensor structure 1012 shown inFIG. 10B. Looking to FIG. 10D, a view of the sensor structure 1012 isshown along a plane perpendicular to the plane of deposition thereof(the same plane of view as shown in FIG. 10C). Although the sensor caplayer 1024 is in full view, portions of the other layers are alsovisible along the cross-track direction 1052 in FIG. 10D due to thesensor structure's flared profile shown in FIG. 10B. As described abovefor the free layer, it is preferred that the height H_(SS) of the sensorstructure 1012 is less than the width W_(SS) of the sensor structure1012. According to some approaches, the height H_(SS) of the sensorstructure 1012 may be less than about 0.8 times the width W_(SS) of thesensor structure 1012. More preferably, in some approaches the heightH_(SS) of the sensor structure 1012 may be less than about 0.5 times thewidth W_(SS) of the sensor structure 1012, but could be higher or lowerdepending on the desired embodiment. This general shape of the sensorstructure 1012 may desirably provide improved sensor performance andoverall increased efficiency of a magnetic head as a result of shapeanisotropy, e.g., as described above in relation to the height H_(FL)and width W_(FL) of the free layer 1026 in FIG. 10C.

Although tunnel valve read transducers having slab dimensions which forma largely homogeneous single magnetic domain aligned along thecross-track direction of the free layer as a result of shape anisotropyalone are desirable, performance may further be improved by implementinghard bias magnets in some embodiments. As mentioned above, hard biasmagnets may be used to further stabilize a free layer and reducemagnetic switching noise. Looking to FIG. 10E, a tunnel valve readtransducer 1070 is shown in accordance with one embodiment. As anoption, the present tunnel valve read transducer 1070 may be implementedin conjunction with features from any other embodiment listed herein,such as those described with reference to the other FIGS. Specifically,FIG. 10E illustrate variations of the embodiment of FIG. 10B depictingseveral exemplary configurations within a tunnel valve read transducer1070. Accordingly, various components of FIG. 10E have common numberingwith those of FIG. 10B.

However, such tunnel valve read transducer 1070 and others presentedherein may be used in various applications and/or in permutations whichmay or may not be specifically described in the illustrative embodimentslisted herein. Further, the tunnel valve read transducer 1070 presentedherein may be used in any desired environment. Thus FIG. 10E (and theother FIGS.) may be deemed to include any possible permutation.

As shown, the tunnel valve read transducer 1070 includes upper and lowershields 1014, 1016, a sensor structure 1012, as well as upper and lowerconducting spacer layers 1018, 1020 positioned between the sensorstructure 1012 and the magnetic shields 1014, 1016, respectively.

Furthermore, the sensor structure 1012 is sandwiched laterally along thecross-track direction 1052, by a pair of hard bias magnets 1032. Inother words, the hard bias magnets 1032 are positioned proximate to aside of the sensor structure 1012 along a cross-track direction 1052 onopposite sides thereof. In preferred approaches, the hard bias magnets1032 include cobalt-platinum. Although chrome may also be implemented inthe hard bias magnets 1032 (e.g., to provide added corrosionprotection), cobalt-platinum-chrome hard bias magnets 1032 may reducethe achievable magnetic moment thereof, and thereby may not be desirablein some approaches. Moreover, other hard bias materials which wouldbecome apparent to one skilled in the art after reading the presentdescription may be implemented in still other approaches.

Moreover, electrically insulating layers 1034 are included on oppositesides of the sensor structure 1012. More specifically, an electricallyinsulating layer 1034 separates each of the hard bias magnets 1032 fromthe sensor structure 1012 and the lower conducting spacer layer 1020, toavoid electrical shorting therebetween. A seed layer 1044 is alsopresent between each of the hard bias magnets 1032 and the respectiveelectrically insulating layers 1034 which may be used to form hard biasmagnets 1032 having an at least partially crystalline composition, e.g.,as will be described in further detail below.

Although the insulating layer 1034 is positioned between each of thehard bias magnets 1032 and the sensor structure 1012, each of the hardbias magnets 1032 are preferably magnetically coupled to (e.g., are inmagnetic communication with) the free layer 1026 sandwichedtherebetween. As would be appreciated by one skilled in the art,magnetic coupling may be achieved between two layers when the layershave proper characteristics. For instance, magnetic coupling may beachieved between two layers in response to the two layers beingpositioned sufficiently close to each other. As mentioned above, thethickness of the electrically insulating layers 1034 may be less thanabout 8 nm, but may be higher or lower depending on the desiredembodiment. Accordingly, the distance D between an edge of each of thehard bias magnets 1032 closest to the free layer 1026 and an edge of thefree layer 1026 closest thereto (e.g., the isolation gap) is preferablybetween about 3 nm and about 7 nm, but could be higher or lowerdepending on other characteristics of the particular tunnel valve readtransducer 1006 structure. For example, proper characteristics forachieving magnetic coupling between two layers may include any one ormore of: having the proper material composition(s), having properdimensions, having proper performance parameters, etc., e.g., as willsoon become apparent.

As alluded to above, the construction of the hard bias magnetsimplemented in a given magnetic tape head were found by the inventors tohave a significant impact on the performance of the overall magnetictape head. The inventors were surprised to discover that by increasing athickness of the hard bias magnets above what was previously consideredto be adequate resulted in a very low incidence of noisy tracks.Previously, it was believed that increasing the thickness of the hardbias layers beyond a certain thickness would actually degrade readperformance by causing a detrimental amount of hard bias flux topermeate the free layer and sensor shields, thereby reducing readbacksignal strengths. In sharp contrast, the improvements included hereinwere surprisingly achieved, at least in part, by the increasedmagnetization from the thicker hard bias magnets effectively stabilizingthe magnetic domains of the free layer near the lateral edges thereof.Moreover, magnetic tape heads implementing these thicker hard biasmagnets were also surprisingly discovered to be tolerant to variation inother aspects of the sensor, e.g., such as free layer magnetostrictionand/or pinned layer design. Thus, by implementing non-intuitive hardbias magnet structures which go directly against conventional wisdom,the inventors were able to realize significant improvements in theperformance of free layers in tunnel valve read transducers.

Specifically, referring still to FIG. 10E, the inventors were surprisedto discover that implementing hard bias magnets 1032 having a depositionthickness t₂ that is 13 or more times greater than a depositionthickness t₃ of the free layer 1026 results in substantial improvementsto the magnetization stability of the free layer 1026 (e.g., see graph1200 of FIG. 12 below). Without wishing to be bound by any theory, theinventors believe that this surprising result is achieved because thethicker hard bias magnets 1032 are able to overcome the loss of field atthe ends of the hard bias magnets 1032 due to magnetic flux leakage intothe magnetic shields 1014, 1016 over the relatively large dimensions(e.g., large widths) of the tape transducer layers. It follows that, adeposition thickness t₂ of each of the hard bias magnets 1032 at about athickest portion thereof is preferably at least 8 times, more preferablyat least 10 times, more preferably at least 13 times greater than adeposition thickness t₃ of the free layer 1026. In some embodiments, thethickness of the hard bias magnets may be expressed as a multiple of thethickness of the free layer times the ratio of the magnetic moment ofthe free layer divided by the magnetic moment of the hard bias magnets.Accordingly, the inventors found that while conventionally this ratio isabout 8, a ratio of about 16 may be implemented for stabilizing the freelayer. According to one approach, a thickness of the hard bias magnetsat a thickest portion thereof may be at least 12 times greater than athickness of the free layer times a ratio of the magnetic moment of thefree layer divided by the magnetic moment of the respective hard biasmagnet. As a result, the hard bias magnets 1032 may serve as a magneticstabilization structure having a sufficient magnetic remnant. Accordingto another approach, the deposition thickness t₂ of each of the hardbias magnets 1032 at about a thickest portion thereof may be about 84.5nm, while the deposition thickness t₂ of the free layer 1026 is about6.5 nm. In preferred approaches, the deposition thickness t₃ of the freelayer 1026 is at least 4 nm. However, it should be noted that thethickness t₂ of each of the hard bias magnets 1032 at about a thickestportion thereof may be higher or lower, e.g., depending on the materialcomposition of the layer.

Moreover, the deposition thickness of each of the hard bias magnets 1032may diminish toward the free layer 1026, thereby resulting in a taperedprofile of the hard bias magnets 1032 toward the free layer 1026.According to an exemplary approach, the taper length of the hard biasmagnets 1032 may be less than the maximum thickness t₂ of each of thehard bias magnets 1032. However, a deposition thickness t₄ of each ofthe hard bias magnets 1032 at an edge closest to the free layer 1026 ispreferably at least greater than the deposition thickness t₃ of the freelayer 1026. As a result, a significant amount of hard bias material ispresent at the interface between each of the hard bias magnets 1032 andthe free layer 1026, thereby increasing the total amount of flux densitythat may be produced from the edge of the hard bias magnets 1032.

It is also preferred that the a first portion of each of the hard biasmagnets 1032 is positioned below a lower surface of the free layer 1026,and a second portion of each of the hard bias magnets 1032 is positionedabove an upper surface of the free layer 1026. Referring to the presentdescription, the terms “lower”/“below” and “upper”/“above” are intendedto be relative to each other along a deposition direction of the layers,the deposition direction being parallel to the intended direction oftape travel 1050 in the present embodiment. In other words, it isdesirable that the edge of each of the hard bias magnets 1032 facing thefree layer 1026 overlaps the free layer 1026 along the intendeddirection of tape travel 1050, and may even be about centered relativeto the free layer 1026 along the deposition direction, e.g., as shown inFIG. 10E.

The edge of each of the hard bias magnets 1032 closest to the free layer1026 preferably has about a vertical profile. In other words, it isdesirable that the edge of each of the hard bias magnets 1032 closest tothe free layer 1026 is oriented at an angle σ relative to a plane ofdeposition of the free layer, where the angle σ may be in a range fromabout 65° to about 105°, more preferably in a range from about 70° toabout 95°, ideally in a range from about 70° to about 90°. Byimplementing hard bias magnets 1032 having an edge closest to the freelayer 1026 that is sufficiently vertical relative to ahorizontally-oriented plane of deposition of the free layer,magnetization of the free layer 1026 is significantly improved as aresult (e.g., see graph 1200 of FIG. 12 below). However, the angle σ ofone or more of the hard bias magnets 1032 may be higher or lowerdepending on the desired embodiment. Furthermore, a free layer 1026having edges facing the hard bias magnets which are about perpendicular(e.g., between about 80° and about 100°) relative to a plane ofdeposition thereof may also improve magnetization of the free layer1026.

Performance of the overall apparatus 1000 may further be improved byimplementing desirable characteristics of the other components (e.g.,layers) as well. In other words, by further improving performance ofeach of the tunnel valve read transducers 1006 themselves, performanceof the magnetic tape head 1002 may improve as well.

Accordingly, in some embodiments the magnetostriction value of each ofthe tunnel valve read transducers 1006 may be adjusted to a desirablevalue, e.g., by implementing processing steps for each of the tunnelvalve read transducers 1006 which would become apparent to one skilledin the art after reading the present description. According to preferredapproaches, the magnetostriction value for the free layer 1026 of eachof the tunnel valve read transducers 1006 is negative. An illustrativerange of the magnetostriction value for any one of the tunnel valve readtransducers 1006 (or specific layer thereof) may be between about −5e⁻⁶and about −1e⁻⁶, but could be higher or lower.

Moreover, in some embodiments the tunnel barrier resistivity (RA) valueof the tunnel barrier layer 1028 in each of the tunnel valve readtransducers 1006 may be adjusted to a desirable value, e.g., byimplementing processing steps for each of the tunnel barrier layer 1028which would become apparent to one skilled in the art after reading thepresent description. According to preferred approaches, each of thetunnel valve read transducers 1006 may have a tunnel barrier layer 1028with a RA value between about 5 Ω/μm² and about 50 Ω/μm², but may bebetween about 10 Ω/μm² and about 40 Ω/μm², but could be higher or lower.

In some embodiments the surface finish roughness of the media facingsurface may also have an effect on the performance of the magnetic tapehead 1002 as a whole. Without wishing to be bound by any theory, theinventors discovered that when average surface finish roughness of theresulting structure is greater than a certain amount, a higher incidenceof noise is observed. Thus, when forming the magnetic tape head 1002and/or the read module 1004 thereof, the media facing surface 1005 maybe processed accordingly in order to achieve an average surface finishroughness (surface roughness) of less than about 20 angstroms (Å), butcould be higher or lower. Processing steps to achieve an average surfacefinish roughness of less than about 20 Å may include any operation whichwould become apparent to one skilled in the art after reading thepresent description. For example, an average surface finish roughness ofless than about 20 Å for the media facing surface 1005 may be realized(e.g., measured) at a point after final mechanical lapping of the mediafacing surface 1005 has been performed.

Further still, it should be noted that in other embodiments, the shapeand thickness of the hard bias magnets 1032 may be selected to result inimproved coupling of magnetic flux into the free layer 1026.Accordingly, depending upon the thickness t₃ of the free layer 1026, themagnetic flux from the hard bias magnets 1032 may serve to reduce theoutput of the free layer 1026 in response to recorded data on a tape.While not ideal in terms of signal output, such designs may be moremagnetically stable.

Referring momentarily to FIGS. 11A-11C, three different hard bias magnetconfigurations are illustrated relative to a free layer. Moreover, graph1200 of FIG. 12 includes plots showing magnetization of the free layervs. the distance from the sensor edge (along the width of the freelayer) for each of the three configurations in FIGS. 11A-11C. It shouldbe noted that the plots included in graph 1200 were obtained usingfinite element analysis, and well-known materials properties for thefree layer and hard bias magnets, while keeping the variablestherebetween equal, other than the geometric differences of the hardbias and free layers as described below.

Looking first to FIG. 11A, the hard bias structure 1102 included thereinis consistent with conventional hard bias structures. As shown, the hardbias structure 1102 is only slightly thicker than the free layer 1104,and the hard bias structure 1102 oriented almost entirely above the freelayer 1104. As illustrated by the corresponding plot in graph 1200 ofFIG. 12, the resulting magnetization of the free layer is adversely low.Moreover, the magnetization of the free layer makes an adverse dipbefore rising to a maximum value at the distance of about 50 nm.

Conversely, FIG. 11B includes a hard bias magnet 1112 which has amaximum thickness that is much greater than the thickness of the freelayer 1114, e.g., according to any of the approaches included herein.The corresponding plot in graph 1200 of FIG. 12 illustrates that theincreased thickness of the hard bias magnet 1112 desirably causes asignificant increase to the magnetization of the free layer 1114,thereby improving the magnetic stability of the free layer 1114,particularly at its lateral edge. Although the resulting increase to themagnetization of the free layer 1114 is desirable, the plot in graph1200 corresponding to the structure of FIG. 11B still includes anundesirable dip before rising to a maximum value at the distance ofabout 75 nm.

However, as described above, the inventors discovered that by orientingthe hard bias magnet such that it is about centered with the free layeralong the deposition direction and/or by making an edge of the hard biasmagnet facing the free layer about perpendicular to the plane ofdeposition, even greater improvements may be achieved. Accordingly, theembodiment illustrated in FIG. 11C illustrates a hard bias magnet 1122which is about centered with the free layer 1124 along the depositiondirection 1126. The hard bias magnet 1122 also has an edge facing thefree layer which is about perpendicular to the plane of deposition (orabout parallel to the deposition direction 1126). Moreover, by formingthe free layer 1124 such that an edge thereof facing the hard biasmagnet 1122 is also about perpendicular to the plane of deposition,performance may even further be improved. As a result, the correspondingplot in graph 1200 of FIG. 12 indicates significant improvements to themagnetization of the free layer relative to what was conventionallyachievable (see plot for FIG. 11A), while also eliminating thepreviously experienced dip in the magnetization of the free layer. Itfollows that various embodiments described herein were surprisinglydiscovered by the inventors to provide a sufficient magnetic field tostabilize the free layer and reduce magnetic noise.

Referring again to FIG. 10E, the hard bias magnets 1032 may be formed tohave different dimensions (e.g., a different structure) according tovarious approaches. However, according to preferred approaches, the hardbias magnets 1032 included herein are formed such that the magneticfield produced by each of the hard bias magnets 1032 is close to amaximum achievable value. In other words, each of the hard bias magnets1032 is preferably characterized as producing a magnetic field that isgreater than or equal to 90% of a maximum achievable magnetic field forthe material of the respective hard bias magnet 1032. Producing amagnetic field close to the maximum achievable magnetic field for thematerial of the respective hard bias magnet 1032 may be accomplished byimplementing favored (e.g., ideal) processing steps during themanufacture thereof, e.g., such as ensuring proper seed layer templatedgrowth, performing a proper annealing process on the resultingstructure, etc.

Referring momentarily to FIG. 10F, a view of the hard bias magnets 1032and free layer 1026 of FIG. 10E are shown along a plane perpendicular tothe plane of deposition of the hard bias magnets 1032 and the free layer1026. Arrows indicating the cross-track direction 1052 and the intendeddirection of tape travel 1050 have been added for reference. As shown,the width W_(HB) of the hard bias magnets 1032 are measured in thecross-track direction 1052. Moreover, according to preferredembodiments, the width of the hard bias magnets 1032 is at least about0.3 μm, but could be higher or lower depending on the desiredembodiment.

Referring again to FIG. 10E, according to some approaches, performancemay further be improved by ensuring material composition integrityduring the formation of the hard bias magnets 1032. Each of the hardbias magnets 1032 are preferably at least partially crystalline. Inother words, the hard bias magnets 1032 may be formed in such a way thatthe material composition thereof is crystalline in nature.

As previously mentioned, the hard bias magnets 1032 in FIG. 10E may havean at least partially crystalline material composition. A hard biasmagnet 1032 having a crystalline material composition may be formed byfirst depositing a seed layer 1044, and then forming the hard biasmagnet layer 1032 from the seed layer 1044. By using the seed layer 1044as a base, the hard bias magnet layer 1032 may desirably form such thatthe material composition thereof is crystalline in nature.

Accordingly, the hard bias magnet 1032 may be formed in full above theseed layer in some approaches. However, crystalline structure growth maybecome less uniform as the hard bias magnet becomes thicker, and thedistance from the seed layer increases. Thus, in some approaches,additional seed layers may be implemented to avoid structuraldegradations caused by a loss of templating. In one such approach, ahard bias magnet may be a split hard bias structure which includes twoseed layers, each of the seed layers having an at least partiallycrystalline structure formed thereabove.

Referring momentarily now to FIG. 10G, a tunnel valve read transducer1080 having a split hard bias magnets 1060 having a crystalline materialcomposition may be formed by first depositing a seed layer 1062, andthen forming a first hard bias layer 1064 from the seed layer 1062,e.g., as described above. Once a portion, e.g., about one half, of thetotal hard bias magnet 1060 has been formed, formation of the first hardbias layer 1064 may be stopped, and a second seed layer 1066 isdeposited on an upper surface of the first hard bias layer 1064 asshown. Thereafter, a second hard bias layer 1068 may be formed from thesecond seed layer 1066. The first and second hard bias layers 1064, 1068may be formed using a same or similar materials, e.g., depending on thedesired embodiment. It should be additionally noted that FIG. 10Gillustrates variations of the embodiment of FIG. 10E depicting anexemplary configuration within a magnetic tape head 1002. Accordingly,various components of FIG. 10G also have common numbering with those ofFIG. 10E.

As mentioned above, shape anisotropy achieved by free layer dimensionsand/or dimensions of the sensor structure as a whole were able toimprove overall performance of various tunnel valve read transducersdescribed herein. Furthermore, hard bias magnets according to variousembodiments described herein were surprisingly discovered by theinventors to provide a magnetic field that more effectively stabilizesthe free layer. Without wishing to be bound by any theory, the inventorsbelieve that this surprising result is achieved because the thicker hardbias magnets are able to overcome the loss of field at the ends of thehard bias magnets due to magnetic flux leakage into the magnetic shieldsover the larger dimensions (e.g., width and/or length) of the tapetransducer.

Accordingly, some of the embodiments included herein are successfullyable to significantly reduce magnetic noise in magnetic tape headsconventionally caused by thermally and/or magnetically induced switchingof unstable domains in a tunnel valve free layer. As a result, magnetictape heads implemented according to any of the approaches describedabove may be able to achieve magnetic stabilization structure thatensures noise due to magnetic instability is less than approximately 1part in 3300, thereby desirably resulting in a less than 1% magnetictape module rejection rate despite previous doubts in the industry thatstructures this efficient were even achievable.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. An apparatus, comprising: a plurality of tunnelvalve read transducers arranged in an array extending along a readmodule, wherein each of the tunnel valve read transducers includes: asensor structure having a cap layer, a free layer, a tunnel barrierlayer, a reference layer and an antiferromagnetic layer; andelectrically insulating layers on opposite sides of the sensorstructure, wherein a height of the free layer measured in a directionperpendicular to a media bearing surface of the read module is less thana width of the free layer measured in a cross-track directionperpendicular to an intended direction of media travel.
 2. The apparatusas recited in claim 1, comprising: an upper conducting spacer layerbetween the sensor structure and an upper magnetic shield; and a lowerconducting spacer layer between the sensor structure and a lowermagnetic shield, wherein the electrically insulating layers separate theupper conducting spacer layer from the lower conducting spacer layer andfrom the opposite sides of the sensor structure.
 3. The apparatus asrecited in claim 1, wherein the plurality of tunnel valve readtransducers includes 35 tunnel valve read transducers.
 4. The apparatusas recited in claim 1, wherein a width of the free layer of each of thetunnel valve read transducers is between about 0.3 μm and about 1.5 μm.5. The apparatus as recited in claim 1, wherein each of the tunnel valveread transducers has a magnetostriction value between about −5e⁻⁶ andabout −1e⁻⁶.
 6. The apparatus as recited in claim 1, wherein each of thetunnel valve read transducers has a tunnel barrier resistivity betweenabout 5 Ω/μm² and about 50 Ω/μ m².
 7. The apparatus as recited in claim1, wherein a media facing surface of the read module has an averagesurface roughness of less than about 20 Å.
 8. The apparatus as recitedin claim 1, wherein each of the tunnel valve read transducers includes:a hard bias magnet, wherein the hard bias magnet is positioned proximateto a side of the sensor structure along a cross-track direction, whereinthe electrically insulating layers separate the hard bias magnet fromthe sensor structure and a lower conducting spacer layer, wherein thelower conducting spacer layer is positioned between the sensor structureand a lower magnetic shield.
 9. The apparatus as recited in claim 8,wherein a distance between an edge of each of the hard bias magnetsclosest to the associated free layer and an edge of the free layerclosest thereto is between about 3 nm and about 7 nm.
 10. The apparatusas recited in claim 8, wherein an edge of each of the hard bias magnetsclosest to the free layer is oriented between 70° and 90° relative to aplane of deposition of the free layer.
 11. The apparatus as recited inclaim 8, wherein a thickness of the free layer is at least 4 nm.
 12. Theapparatus as recited in claim 8, wherein the hard bias magnet is a splithard bias structure having two seed layers, each of the seed layershaving an at least partially crystalline structure formed thereabove.13. The apparatus as recited in claim 8, wherein a thickness of the hardbias magnet at a thickest portion thereof is at least 12 times greaterthan a thickness of the free layer times a ratio of a magnetic moment ofthe free layer divided by a magnetic moment of the hard bias magnet. 14.The apparatus as recited in claim 8, wherein a thickness of the hardbias magnet at an edge closest to the free layer is greater than thethickness of the free layer.
 15. The apparatus as recited in claim 14,wherein a first portion of each of the hard bias magnet is positionedbelow a lower surface of the free layer and a second portion of the hardbias magnet is positioned above an upper surface of the free layer,wherein the upper and lower surfaces are opposite each other along adeposition direction.
 16. The apparatus as recited in claim 8, wherein awidth of the hard bias magnet measured in the cross-track direction isat least 0.3 μm.
 17. The apparatus as recited in claim 1, wherein theheight of the sensor structure is less than 0.8 times the width of thesensor structure.
 18. The apparatus as recited in claim 1, comprising:an upper magnetic shield; and a lower magnetic shield, wherein aseparation between the upper and lower magnetic shields proximate to thesensor structure and along the intended direction of media travel isless than 120 nm.
 19. The apparatus as recited in claim 1, wherein theplurality of tunnel valve read transducers share a common media facingsurface of the read module.
 20. The apparatus as recited in claim 1,comprising: a drive mechanism for passing a magnetic medium over thetunnel valve read transducers; and a controller electrically coupled tothe tunnel valve read transducers.